1. Field of the Invention
The invention relates to a continuously variable transmission having two pulleys, each formed of a stationary sheave and a movable sheave, and a belt disposed on the two pulleys and, more particularly, to a support construction for a stationary sheave of a continuously variable transmission suitable for use in a motor vehicle.
2. Description of the Related Art
A continuously variable transmission is disclosed in U.S. Pat. No. 4,680,711. As shown in FIG. 1 here, this prior art continuously variable transmission 200 includes a primary pulley 202 and a secondary pulley 203 that are rotatably supported by a case 201, and a belt 205 disposed on the pulleys 202, 203. Each pulley is formed of a stationary sheave 206 or 207 and a movable sheave 209 or 210. The movable sheaves 209 and 210 are axially moved by hydraulic actuators 211 and 212, respectively.
The primary-side hydraulic actuator 211 has a cylinder member 213, and an annular member 216 disposed on the movable sheave 209 so that a hydraulic chamber 215 is formed between the annular member 216 and the cylinder member 213. The movable sheave 209 is moved by supplying hydraulic pressure into the hydraulic chamber 215 to effect a "shift."
The cylinder member 213 is fitted over a boss portion 206a of the stationary sheave 206. On the rear side of the cylinder member 213, a washer 220 is fitted over the boss portion 206a. A bearing 221 for rotatably supporting the stationary sheave 206 and a nut 222 for fixing these members in position are also fitted over the boss portion 206a of the stationary sheave 206.
However, the continuously variable transmission 200 has the problem of a large axial dimension, i.e. the dimension set by the rotating axes of the transmission, due to the presence of the washer 220 and the bearing 221 disposed between the cylinder member 213 and the nut 222.
To reduce the axial dimension of the transmission, the washer 220 can be omitted. However, because the washer 220 serves as a reinforcement for the cylinder member 213, which bears high hydraulic pressure within the hydraulic chamber 215, omission of the washer 220 will create a new problem in that the base end portion of the cylinder member 213 contacting the boss portion 206a may deform.
To prevent deformation of the cylinder member 213 with omission of the washer 220, several approaches are possible, for example:
(1) the plate thickness of the cylinder member may be increased;
(2) a stronger material may be used to form the cylinder member; and
(3) the cylinder member may be subjected to an appropriate heat treatment.
However, (1) still has the problem of increased axial dimension and (2) and (3) have problems of increased cost of component parts and overall production.